FR2949776A1 - LAYERED ELEMENT FOR ENCAPSULATING A SENSITIVE ELEMENT - Google Patents

Abstract

This layered element (11) for the encapsulation of an element (12) sensitive to air and / or humidity, in particular a collector element or radiation emitter such as a photovoltaic cell or an organic light-emitting diode, comprises a polymer layer (1) and a barrier layer (2) against at least one face (1A) of the polymer layer. The barrier layer (2) consists of a stack of at least two thin layers (21, 22, 23, 24) of hydrogenated silicon nitride having alternatively lower and higher densities.

Description

The present invention relates to a layered element for the encapsulation of an element sensitive to air and / or humidity, in particular a collector element or emitter of radiation. such as a photovoltaic cell or an organic light emitting diode. The invention also relates to a collector or radiation emitter device comprising such a layered element, as well as to a method of manufacturing such a layered element. A radiation collecting device is, in particular, a photovoltaic module comprising at least one photovoltaic cell capable of collecting and converting the energy resulting from radiation into electrical energy. A radiation emitting device is, in particular, an OLED device comprising at least one organic light-emitting diode, or OLED, capable of converting electrical energy into radiation. In known manner, the energy conversion elements of a collector device or radiation emitter, namely the photovoltaic cells in the case of a photovoltaic module or the OLED structures in the case of an OLED device, comprise a material adapted to ensure the conversion of energy and two electrically conductive contacts on either side of this material. However, whatever their manufacturing technology, these energy conversion elements are likely to be degraded under the effect of environmental conditions, especially under the effect of exposure to air or moisture. By way of example, for OLED structures or organic photovoltaic cells, the front electrode and the organic material are particularly sensitive to environmental conditions. For thin-film photovoltaic cells comprising an inorganic absorber layer, the front electrode of the cell, formed on the basis of a transparent conductive oxide (TCO) layer or a metal layer transparent (Transparent Conductive Coating or TCC), is also very sensitive to environmental conditions.

In order to protect the energy conversion elements of a collector device or radiation emitter against damage due to exposure to air or moisture, it is known to manufacture the device with a structure laminate, wherein the energy conversion elements are encapsulated and associated with a front substrate, or glass-backed substrate, as well as optionally with a back substrate, or substrate with a support function. Depending on the application of the device, the front and rear substrates may in particular be made of a transparent glass or a transparent thermoplastic polymer, for example polyethylene, polyester, polyamide, polyimide, polycarbonate, polyurethane, polymethylmethacrylate, or a fluoropolymer. In the case of a photovoltaic cell comprising an absorber layer based on chalcopyrite compound, in particular comprising copper, indium and selenium, said CIS absorber layer, possibly containing gallium (CIGS absorber layer ), aluminum or sulfur, a polymeric lamination interlayer is positioned between the front electrode and the front substrate, to ensure good cohesion of the module during its assembly, including rolling. It has been found, however, that when a collector or radiation emitter device comprises a polymeric lamination interlayer or a polymer substrate positioned against an air-sensitive energy conversion element and / or moisture, the present device a significant degradation rate. Indeed, the presence of the lamination interlayer, which tends to store moisture, or the polymeric substrate, which has a high permeability, promotes the migration of polluting species such as water vapor or water. oxygen to the sensitive element, and thus the alteration of the properties of this element. It is these disadvantages that the invention intends to remedy more particularly by proposing a layered element which, when integrated in a collector device or emitter of radiation, gives this device improved resistance, especially to air and moisture, providing effective and long-term protection of energy conversion elements of the device that are sensitive to air and / or moisture. For this purpose, the subject of the invention is a layered element for the encapsulation of an element sensitive to air and / or humidity, in particular a collector element or emitter of radiation such as a photovoltaic cell or a organic light-emitting diode, the layered element comprising a polymer layer and a barrier layer against at least one side of the polymer layer, characterized in that the or each barrier layer consists of a stack of at least two thin layers of nitride, hydrogenated silicon having alternately lower and stronger densities. For the purposes of the invention, thin film is understood to mean a layer of thickness less than 1 micrometer. Encapsulation of a sensitive element is also understood to mean covering at least a portion of the sensing element so that the sensing element is not exposed to environmental conditions. In addition, in the context of the invention, a layered element is a set of layers arranged against each other, without prejudging any order of deposition of the constituent layers of the element on each other. According to other advantageous characteristics of a layered element according to the invention, taken individually or in any technically possible combination: the or each barrier layer comprises, at the interface between a first layer and a second layer of each pair successive thin layers of its constituent stack, a junction zone having a density gradient between the density of the first layer and the density of the second layer; the difference between the density of a layer of higher density and the density of a lower density layer of each pair of successive thin layers of the constituent stack of the or each barrier layer is greater than or equal to 10% the density of the lower density layer; the layered element comprises a barrier layer against the face of the polymer layer intended to be directed towards the sensing element side and / or a barrier layer against the face of the polymer layer intended to be directed away from the the sensitive element; the polymer layer is a thermoplastic polymer substrate which comprises a barrier layer on at least one of its faces; the polymer layer is a lamination interlayer which comprises a barrier layer against at least one of its faces; the polymer layer and the or each barrier layer are transparent, the geometric thickness of each thin layer of the or each barrier layer being adapted to maximize the transmission of radiation through the layered element, to or from the sensitive element, by an anti-reflective effect; the constituent stack of the or each barrier layer comprises at least the superposition of a thin layer of hydrogenated silicon nitride with a refractive index between 1.8 and 1.9 at 550 nm and a thin layer of hydrogenated silicon nitride of refractive index between 1.7 and 1.8 at 550 nm. Within the meaning of the invention, when the layered element is intended to be integrated in the front face of a collector device or emitter of radiation, a layer is considered to be transparent when it is transparent at least in the length domains of wave useful for, or emitted by, the collector elements or radiation emitters of the device. By way of example, in the case of a photovoltaic module comprising photovoltaic cells based on polycrystalline silicon, each transparent layer is advantageously transparent in the wavelength range between 400 nm and 1200 nm, which are the lengths. useful for this type of cell. The invention also relates to a device comprising an air sensitive element and / or moisture and a layered element as described above as a front and / or rear encapsulation element of the sensitive element. Advantageously, the device is a collector device or emitter of radiation, the sensitive element being a collector element or emitter of radiation, which is arranged with respect to the layered element so as to be able to collect radiation crossing the polymer layer and the or each barrier layer, or to emit radiation through the polymer layer and the or each barrier layer. In particular, the collector element or radiation emitter may be a photovoltaic cell or an organic light-emitting diode.

Finally, the subject of the invention is a method for manufacturing a layered element as described above, in which at least a portion of the thin layers of the constituent stack of the or each barrier layer are deposited by chemical deposition. plasma-assisted vapor phase (PECVD) and / or sputtering. In particular, at least a portion of the thin layers of the constituent stack of the or each barrier layer may be deposited by plasma-assisted chemical vapor deposition by varying during the deposition the pressure in the enclosure of the deposit and / or the power and / or the relative proportions of the precursors. It is also possible to deposit at least a portion of the thin layers of the constituent stack of the or each barrier layer by cathode sputtering, in particular assisted by a magnetic field, by varying during the deposition the pressure in the chamber of the deposit and / or the power.

Advantageously, in the case where the thin layers of the constituent stack of the or each barrier layer are deposited on one side of a thermoplastic polymer substrate, the substrate face is activated prior to deposition by means of a plasma, for example a plasma of O2 or H2.

The characteristics and advantages of the invention will appear in the following description of four embodiments of a layered element according to the invention, given solely by way of example and with reference to the appended drawings in which: Figure 1 is a schematic cross section of a photovoltaic solar module comprising a layered element according to a first embodiment of the invention; FIG. 2 is a section similar to FIG. 1 for an OLED device comprising the layered element of FIG. 1; FIG. 3 is a view on a larger scale of the layered element of FIGS. 1 and 2; FIG. 4 is a view similar to FIG. 3 for a layered element according to a second embodiment of the invention; FIG. 5 is a view similar to FIG. 3 for a layered element according to a third embodiment of the invention; FIG. 6 is a section similar to FIG. 1 for a photovoltaic solar module comprising a layered element according to a fourth embodiment of the invention; and FIG. 7 is a view on a larger scale of the layered element of FIG. 6. Throughout this description, the numerical values of refractive indices are given at 550 nm under illuminant D65, in FIG. DIN 67507. The photovoltaic solar module 50 shown in FIG. 1 is a thin-film photovoltaic module, comprising a glass-fronted front substrate 1 and a back-up substrate 8, between which a stack of layers 2, 4 is arranged. , 5, 6, 7. The front substrate 1, intended to be arranged on the side of incidence of solar radiation on the module 50, is made of a transparent thermoplastic polymer, in particular, in this example, polyethylene terephthalate (PET), and has a geometric thickness of 200 micrometers. The rear substrate 8 is made of any suitable material, transparent or not, and carries, on its face facing the inside of the module 50, that is to say on the side of incidence of solar radiation on the module, a electrically conductive layer 7 which forms a rear electrode of the photovoltaic cell 12 of the module 50. By way of example, the layer 7 is based on molybdenum. The back electrode layer 7 is conventionally surmounted by a layer of absorber 6 composed of chalcopyrite, in particular CIS or CIGS, capable of ensuring the conversion of solar energy into electrical energy. The absorber layer 6 is itself surmounted by a CdS cadmium sulphide layer, not shown in the figures and possibly associated with an undoped intrinsic ZnO layer, also not shown, and then by an electrically conductive layer which forms a front electrode of the cell 12. The photovoltaic cell 12 of the module 50 is thus formed by the stacking of the layers 5, 6 and 7. A polymeric lamination interlayer 4 is positioned between the front electrode layer 5 and the front substrate 1, so as to ensure the maintenance of the functional layers of the module 50 between the substrates before 1 and back 8. The lamination interlayer 4 is a layer of thermosetting polymer, namely a layer of ethylene vinyl acetate (EVA) in this example. Alternatively, the lamination interlayer 4 may be made of polyvinyl butyral (PVB), or any other material of suitable properties.

The front electrode layer 5 of the cell 12 is an aluminum doped zinc oxide (AZO) layer. Alternatively and by way of nonlimiting examples, the layer 5 may be a layer doped with boron doped zinc oxide, a layer based on another doped transparent conductive oxide (TCO), or a transparent metal layer (TCC) such as a silver stack. In all these cases, the front electrode layer 5 is a sensitive layer whose properties are likely to be degraded by exposure to air or moisture. In order to protect the layer 5 from external environmental conditions, the module 50 comprises a barrier layer 2, which is interposed between the lamination interlayer 4 and the front substrate 1 made of PET. The assembly of the substrate 1 and the superimposed barrier layer 2, where the barrier layer 2 is arranged against the face 1A of the substrate 1 intended to be directed towards the inside of the module, forms a layered element 11. In this mode of embodiment, the barrier layer 2 consists of a stack of four thin transparent layers 21, 22, 23, 24 of hydrogenated silicon nitride having both alternatively lower and stronger densities and refractive indices alternatively lower and stronger . The difference between the density d21 = d23 of the layers 21 and 23 of higher density and the density d22 = d24 of the layers 22 and 24 of lower density is of the order of 10% of the density d22 = d24 of the layers 22 and 24 of lower density. Since the layers 21 to 24 are of the same SiNXHy chemical nature, this difference in density is obtained by varying the stoichiometry, that is to say the values of x and / or y, between the denser layers and the less dense layers. . The presence of the lower density layers 22 and 24 makes it possible to relax the stresses at the denser layers 21 and 23, which limits the formation of defects inside the barrier layer 2. In fact, the high densities are often accompanied by strong mechanical stresses within the layer, which can be the origin of the appearance of cracks, which are privileged paths for the diffusion of polluting species such as water vapor or oxygen. In particular, it appears that a layer whose density varies according to its thickness is less likely to generate cracks, and is therefore more effective in terms of protection against the migration of polluting species, such as water vapor and oxygen, a layer of the same thickness, of average density equal or greater, but uniformly dense. The reason is that the succession of domains of different densities interrupts the propagation of cracks. The diffusion paths, and therefore the diffusion times are thus considerably lengthened. In addition, as shown in FIG. 3, for each pair of successive thin layers of the barrier layer 2, the barrier layer comprises, at the interface between the two successive thin layers, a junction zone 20 of geometrical thickness included between 10 nm and 30 nm, preferably between 10 nm and 20 nm, which has a density gradient between the density of a first layer and the density of the second layer of the pair of layers. In other words, each junction zone 20 has, from the lower density layer 22 or 24 to the higher density layer 21 or 23, a density gradient between the lower density d22 = d24 and the higher density. strong d2l = d23. Thanks to the junction zones 20, there is a smooth transition, in terms of density, between the different successive thin layers of the constituent stack of the barrier layer 2. In particular, it can be considered that the variation of the density in the barrier layer 2 is a continuous and periodic variation. This continuous variation of the density in the barrier layer limits the mechanical problems, for example of delamination, which would be likely to occur in the presence of discontinuities or abrupt changes in density at the interface between the successive layers of the constituent stack of the barrier layer.

Advantageously, the barrier layer 2 not only protects the layer 5, but also ensures good radiation transmission to the photovoltaic cell 12. In fact, from an optical point of view, the barrier layer 2 can be optimized to act as an antireflection coating at the interface between the PET substrate 1 and the laminating interlayer 4 made of EVA. A loss of incident radiation on the module 50 occurs at this interface by reflection, because of the difference in refractive indices between the constituent materials of the substrate 1 and the lamination interlayer 4. However, thanks to the refractive indices n21, n22, n23, n24 alternatively weaker and stronger thin layers 21 to 24, and for suitable geometrical thicknesses e21, e22, e23, e24 of these layers, the barrier layer 2 may constitute an interference filter and provide a function antireflection at the interface between the substrate 1 and the lamination interlayer 4. These values adapted geometrical thicknesses of the layers of the constituent stack of the barrier layer 2 may in particular be selected by means of optimization software. By way of example, a stack of the optically optimized barrier layer 2 comprises, successively, from the face 1A of the substrate 1 made of PET to the laminating interlayer 4 made of EVA: a first layer 21 of nitride hydrogenated silicon of relatively higher density d21, having a refractive index n21 of the order of 1.9 and a geometric thickness e21 of between 1 and 20 nm, preferably between 5 and 15 nm, a second layer 22 of silicon nitride hydrogenated relatively low density d22, having a refractive index n22 of the order of 1.7 and a geometric thickness e22 between 25 and 45 nm, preferably between 30 and 40 nm, - a third layer 23 of nitride of hydrogenated silicon of relatively higher density d23 = d21, having a refractive index n23 = n21 of the order of 1.9 and a geometrical thickness e23 of between 55 and 75 nm, preferably between 60 and 70 nm, and - a fourth couch e 24 hydrogenated silicon nitride of relatively lower density d24 = d22, having a refractive index n24 = n22 of the order of 1.7 and a geometric thickness e24 between 65 and 85 nm, preferably between 75 and 85 nm. This particular quadricouche stack is the optically optimized stack, which has a minimum total geometrical thickness, it being understood that other optically optimized quadricouche stacks are also possible, with d thicknesses of the different individual thin layers and a total geometrical thickness of the stack greater than that of the stack described above. An evaluation of the performance of the barrier layer 2 optimized above as a moisture barrier leads to a value of the Moisture Vapor Transfer Rate (MVTR) of the layer 2 of less than 10. -2 g / m2 per day. Thus, the quadricouche barrier layer 2 provides effective protection of the underlying layers of the module 50 against moisture, in particular more effective than a monolayer barrier layer consisting of hydrogenated silicon nitride SiNXHy which would have a geometric thickness equal to total geometric thickness of the barrier layer 2 and constant stoichiometry over the entire thickness of the layer. Indeed, the succession of layers 21 to 24 having alternating densities in the thickness of the barrier layer 2 interrupts the propagation of cracks inside the layer 2. Diffusion paths and pollutant diffusion times , such as water vapor and oxygen, are thus considerably lengthened. Moreover, the reflection of the solar radiation at the interface between the front substrate 1 provided with the barrier layer 2 on its face 1A, so as to form the layer element 11, and the lamination interlayer 4 is less than the reflection that would occur at the interface between a PET substrate and the lamination interlayer 4 in the absence of the barrier layer 2. This results in improved transmission of solar radiation to the absorber layer 6 through the element in layer 11 according to the invention, and therefore a photovoltaic efficiency, or energy conversion efficiency, increased by the module 50 with respect to the photovoltaic efficiency obtained in the absence of the barrier layer 2. FIG. 2 illustrates the case where the layered element 11 shown in Figures 1 and 3 equips an organic electroluminescent device or OLED 60. In known manner, the OLED device 60 successively comprises the substrate before 1 and the barrier layer 2 fo wherein the layered element 11, a first transparent electrode 15, a stack 16 of organic electroluminescent layers and a second electrode 17. The substrate 1 is the front substrate of the device 60, arranged on the radiation extraction side out of the device, the barrier layer 2 being directed towards the inside of the device.

The first electrode 15 comprises a transparent electroconductive coating, such as based on indium tin doped oxide (ITO), or a silver stack. The stack of organic layers 16 comprises a central electroluminescent layer interposed between an electron transport layer and a hole transport layer, themselves interposed between an electron injection layer and a hole injection layer. . The second electrode 17 is made of an electrically conductive material, in particular a metallic material of the silver or aluminum type. As for the module 50, the barrier layer 2 provides both effective protection of the underlying sensitive layers 15, 16 and 17, by preventing the migration of polluting species to these layers, and an optimal radiation transmission from the stacking electroluminescent layers 16 towards the outside of the device 60. In the second embodiment shown in FIG. 4, the elements similar to those of the first embodiment bear identical references increased by 100. The layered element 111 conforms this second embodiment is intended to equip a collector device or radiation emitter, for example a photovoltaic module or an OLED device. The layered element 111 comprises a PET substrate 101 having a geometric thickness of 200 microns and a barrier layer 103 on the substrate face 101B intended to be directed away from the collector element or radiation emitter. Thus, the layered element 111 differs from the layered element 11 of the first embodiment in that the barrier layer is arranged on the face of the substrate intended to be directed opposite the collector element or emitter radiation, and not on the face of the substrate to be directed towards the collector element or radiation emitter. In addition, the barrier layer 103 is a two-layer, and not four-layer, stack which comprises two thin transparent layers 131, 132 of hydrogenated silicon nitride having both alternatively lower and higher densities and refractive indexes which are alternatively lower and stronger. In a similar manner to the first embodiment, the difference between the density d131 of the layer 131 of higher density and the density d132 of the layer 132 of lower density is of the order of 10% of the density d132 of the layer 132 of lower density, this difference in density being obtained by varying the stoichiometry between the two layers 131 and 132 of the same chemical nature SiNXHy. In addition, the barrier layer 103 comprises, at the interface between its two constituent thin layers, a junction zone 130 with a geometric thickness of between 10 nm and 30 nm, preferably between 10 nm and 20 nm, which has, since the layer 131 to the layer 132, a density gradient between the density d131 of the layer 131 and the density d132 of the layer 132. Advantageously, the stack of the barrier layer 103 is also designed with geometric thicknesses e131, e132 and refractive indices n131, n132 of the layers 131 and 132 adapted so that the barrier layer 103 provides an antireflection function at the interface between the PET substrate 101 and the air. The presence of the barrier layer 103 at this interface is all the more effective in maximizing the transmission of radiation through the layered element to or from the energy conversion elements of the device in which the layered element is integrated, that, due to a strong difference in refractive indices between the constituent material of the substrate 101 and the air, the reflection at this interface is important. For example, a bilayer stack of the barrier layer 103 optically optimized, that is to say, to obtain a maximum antireflection effect at the interface between the substrate 101 and the air , while having a minimum total geometrical thickness, comprises successively, from the face 101B of the substrate 101: a first layer 131 of relatively high density hydrogenated silicon nitride d131, having an index of refraction n131 of the order of 1 , 9 and a geometric thickness e131 between 50 and 70 nm, preferably between 60 and 70 nm, and - a second layer 132 of relatively lower density hydrogenated silicon nitride d132, having an index of refraction n132 of the order of 1.7 and a geometric thickness e132 of between 60 and 80 nm, preferably between 70 and 80 nm. As in the first embodiment, this barrier layer 103 provides effective protection of the underlying sensitive layers of a collector device or emitter of radiation against polluting species, in particular more effective than a monolayer barrier layer consisting of nitride of SiNXHy hydrogenated silicon of constant stoichiometry over the entire thickness of the layer, which would have a geometrical thickness equal to the total geometrical thickness of the barrier layer 103. In addition, the barrier layer 103 makes it possible to obtain a reduction in the reflection solar radiation at the interface between the front substrate and the air, with respect to the reflection that would occur at the interface between a PET substrate and the air in the absence of a barrier layer. The gain in terms of reflection rate is of the order of 3%. Thus, it is possible to improve the energy conversion efficiency of a collection device or radiation emitter by incorporating the layered element 111 according to the invention. In the third embodiment shown in FIG. 5, elements similar to those of the first embodiment carry identical references increased by 200. The layered element 211 according to this third embodiment is intended to equip a collecting device. or radiation emitter, for example a photovoltaic module or an OLED device. The layered element 211 comprises a PET substrate 201 having a geometric thickness of 200 micrometers and is distinguished from the layered elements 11 and 111 of the previous embodiments in that it comprises two bilayer barrier layers 202 and 203, deposited respectively on the face 201A of the substrate 201 intended to be directed on the side of the collector element or radiation emitter and on the face 201 B of the substrate 201 intended to be directed opposite the collector element or emitter of radiation .

Each of the two barrier layers 202 and 203 is a stack of two thin transparent layers 221, 222 or 231, 232 of hydrogenated silicon nitride having both alternatively lower and higher densities and refractive indices alternatively lower and higher. strong. As before, the difference between the density of the higher density layers and the density of the lower density layers, which is of the order of 10% of the density of the lower density layers, is obtained for each barrier layer. 202 and 203, by varying the stoichiometry between the two constituent layers of the barrier. In addition, each of the two barrier layers 202 and 203 comprises, at the interface between its two constituent thin layers, a junction zone 220 or 230 of geometrical thickness between 10 nm and 30 nm, preferably between 10 nm and 20 nm. nm, which has a density gradient between the density of a first layer and the density of the second layer of the barrier layer.

The examples of two-layer stacks given below are the barrier layer stacks 202 and 203 making it possible to obtain a maximum antireflection effect at the interface between, respectively, the substrate 201 and an EVA laminating interlayer for the barrier layer 202. and the substrate 201 and the air for the barrier layer 203, while having total geometric thickness values of the two minimum barrier layers. For the barrier layer 202 deposited on the surface 201A of the substrate 201, the optimized stack of minimum geometrical thickness comprises, successively, from the surface 201A of the substrate 201: a first layer 221 of relatively high density hydrogenated silicon nitride d221 , having an index of refraction n221 of the order of 1.9 and a geometrical thickness e221 of between 1 and 20 nm, preferably between 5 and 15 nm, and - a second layer 222 of hydrogenated silicon nitride of relatively higher density. low d222, having a refractive index n222 of the order of 1.7 and a geometric thickness e222 between 100 and 130 nm, preferably between 110 and 125 nm. For the barrier layer 203, deposited on the surface 201B of the substrate 201, the optimized stack successively comprises, from the face 201B of the substrate 201: a first layer 231 of relatively higher density hydrogenated silicon nitride d231, having a subscript n231 refractive index of the order of 1.9 and a geometric thickness e231 between 60 and 80 nm, preferably between 60 and 70 nm, and - a second layer 232 of relatively lower density hydrogenated silicon nitride d232, having a refractive index n232 of the order of 1.7 and a geometric thickness e232 of between 60 and 90 nm, preferably between 70 and 80 nm. The two-layer barrier layer element 211 provides effective protection of underlying critical layers against polluting species and minimization of solar radiation reflection, both at the interface between the layered element and the air and at the interface between the layered element and the underlying layer of a device in which the layered element is integrated.

In the fourth embodiment shown in FIGS. 6 and 7, the elements similar to those of the first embodiment carry identical references increased by 300. The photovoltaic solar module 350 represented in FIG. 6 comprises a front substrate 301 constituted indifferently by glass or transparent thermoplastic polymer. The module 350 also comprises a rear substrate 308 which carries, on its face facing the inside of the module 350, an electrically conductive layer 307 forming a rear electrode of the photovoltaic cell 312 of the module. The layer 307 is surmounted by a layer 306 of absorber material to chalcopyrite compound, in particular CIS or CIGS, suitable for ensuring the conversion of solar energy into electrical energy. Similarly to the first embodiment, the absorber layer 306 is itself surmounted by a layer 305 electrically conductive and sensitive to moisture, based on zinc oxide doped with aluminum (AZO), which forms a front electrode of the cell 312. The photovoltaic cell 312 of the module 350 is thus formed by the stack of the layers 305, 306 and 307. A polymeric lamination interlayer 304 made of EVA, designed to maintain the functional layers of the module 350 between the front 301 and rear 308 substrates, is positioned above the AZO layer 305, against the front substrate 301. Alternatively, the lamination interlayer 304 may be made of PVB, or any other material of properties adapted. In order to protect the AZO layer 305, which is a moisture sensitive layer, from the moisture possibly stored in the lamination interlayer 304, the module 350 comprises a barrier layer 302 interposed between the layers 304 and 305. The layered interlayer layer 304 and the barrier layer 302 form a layered member 311, where the barrier layer 302 is positioned against the face 304A of the layer 304 intended to be directed towards the interior of the module. As in the first embodiment, the barrier layer 302 consists of a stack of four thin transparent layers 321, 322, 323, 324 of hydrogenated silicon nitride having both alternatively lower and higher densities and refractive indices. alternatively weaker and stronger, wherein the geometric thickness of each thin layer of the stack 302 is optically optimized to provide an antireflection effect at the interface between the laminating interlayer layer 304 made of EVA and the AZO layer 305 forming a front electrode. The reduction in the reflection that can be obtained in this fourth embodiment thanks to the barrier layer 302 is particularly important because of the large difference in refractive index between the lamination interlayer and the AZO. As before, the difference between the density of the higher density layers and the density of the lower density layers of the barrier layer 302 is of the order of 10% of the density of the lower density layers. In addition, for each pair of successive thin layers of the barrier layer 302, the barrier layer comprises, at the interface between the two successive layers, a junction zone 320, with a geometric thickness of between 10 nm and 30 nm, of preferably between 10 nm and 20 nm, which has a density gradient between the density of a first layer and the density of the second layer of the pair of layers. By way of example, a four-layer stack of the optically optimized barrier layer 302, that is to say, making it possible to obtain a maximum antireflection effect at the interface between the layer 304 made of EVA and the AZO layer 305, while having a minimum total geometrical thickness, comprises successively, from the face 304A of the laminating interlayer layer 304 to the AZO layer 305: a first layer 321 of relatively high density hydrogenated silicon nitride lower d321, having an index of refraction n131 of the order of 1.7 and a geometrical thickness e321 between 25 and 60 nm, preferably between 35 and 50 nm, - a second layer 322 of hydrogenated silicon nitride of density relatively stronger d322, having an index of refraction n322 of the order of 1.9 and a geometrical thickness e322 of between 100 and 150 nm, preferably between 115 and 140 nm, a third layer 323 of hydrogenated silicon nitride born of relatively lower density d323 = d321, having a refractive index n323 = n321 of the order of 1.7 and a geometrical thickness e323 of between 1 and 30 nm, preferably between 10 and 20 nm, and - a fourth layer 324 of hydrogenated silicon nitride of relatively higher density d324 = d322, having a refractive index n324 = n322 of the order of 1.9 and a geometrical thickness e324 of between 1 and 30 nm, preferably between 10 and 20 nm. The barrier layer 302 has a water vapor transmission rate of less than 10-2 g / m 2 per day and makes it possible to obtain a reduction in the reflection of the solar radiation at the interface between the EVA layer 304 and the layer 305 in AZO corresponding to a gain, in terms of reflection ratio, of the order of 2%. The foregoing examples illustrate the advantages of a layered element according to the invention which, when integrated in a collector or radiation emitter device, gives this device improved resistance to exposure-induced damage. air or moisture, without decreasing the efficiency of energy conversion of the device, or even with an increase in this yield by an anti-reflective effect of the barrier layer of the layered element. The antireflection effect, obtained by adapting the geometrical thicknesses of the various thin layers of hydrogenated silicon nitride constituting the barrier layer, is advantageous but not mandatory. The main function of a layered element according to the invention is to provide effective and long-term protection of the sensitive elements of the device in which it is integrated, namely in particular the energy conversion elements in the case of a collector device or radiation emitter. In particular, a layered element according to the invention can be used for the encapsulation before and / or for the rear encapsulation of an element likely to be degraded under the effect of environmental conditions. In the case where the sensing element is not a collector element or radiation emitter, an antireflection function of the layered element is unnecessary, as well as in the case where the layered element is used for encapsulation rear of a collector element or radiation emitter, in particular a photovoltaic cell or an organic light-emitting diode.

The invention is not limited to the examples described and shown. In general, the aforementioned advantages in terms of protection with respect to the environmental conditions can be obtained by means of any layered element comprising a polymer layer, in particular formed by a thermoplastic polymer substrate or by a polymeric lamination interlayer. thermosetting, and at least one barrier layer consisting of a stack of at least two thin layers of hydrogenated silicon nitride having alternatively lower and higher densities. In particular, in the examples described above, the or each barrier layer is a transparent thin layer. Alternatively, at least one barrier layer of a layered element according to the invention may not be transparent, especially when the layered element is used for the rear encapsulation of a collector element or radiation emitter, or for front and / or rear encapsulation of an element that is susceptible to degradation by environmental conditions but is not a collector or radiation emitter. The characteristics of the thin layers of hydrogenated silicon nitride of the or each barrier layer of a layered element according to the invention may be different from those described above, in particular their refractive indices and their thicknesses. The or each barrier layer of a layered element according to the invention may also comprise any number, greater than or equal to two, superimposed thin layers. Moreover, in the case where the polymer layer of the layered element according to the invention is a thermoplastic polymer substrate, it may be made of any thermoplastic polymer of suitable properties, this thermoplastic polymer being transparent or not transparent. function of the application. Examples of suitable thermoplastic polymers include, in particular, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate, polyurethane, polymethyl methacrylate, polyamides, polyimides, or fluoropolymers such as ethylene tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), ethylene chlorotrifluoroethylene (ECTFE), fluorinated ethylene-propylene copolymers (FEP). Similarly, in the case where the polymer layer is a lamination interlayer, it may consist of any polymer of properties adapted to its function, for example selected from thermosetting polymers, such as EVA or PVB, ionomers, thermoplastic urethanes, adhesives based on polyolefins, thermoplastic silicones. The polymer layer of a layered element according to the invention may also be of any size adapted to its function, in particular of a geometric thickness different from those previously described by way of example. A layered element according to the invention can also be used in any type of device comprising an air-sensitive element and / or humidity, without being limited to the collector devices or radiation emitters described above. In particular, the invention can be applied for the encapsulation of thin-film photovoltaic cells whose absorber layer is a thin layer based on silicon, amorphous or microcrystalline, or based on cadmium telluride, instead of a thin layer of chalcopyrite compound of the CIS or CIGS type. In known manner, in the case where the absorber layer is a CIS or CIGS absorber thin film, the photovoltaic module is manufactured in substrate mode, that is to say by successive deposition of the constituent layers of the cell on the rear substrate of the module. In particular, in the case of the fourth embodiment, the barrier layer 302 is then deposited on the front electrode layer 305. On the contrary, in the case where the absorber layer is a silicon-based thin layer or a cadmium telluride-based thin layer, the photovoltaic module is manufactured in superstrate mode, that is to say by successive deposition. constituent layers of the cell from the front substrate of the module.

The invention can also be applied to organic photovoltaic cell modules, whose organic absorber layer is particularly sensitive to environmental conditions, or to modules whose photovoltaic cells are formed from wafers or polycrystalline or monocrystalline silicon wafers. forming a p / n junction. A layered element according to the invention can also be applied to the photosensitive pigment Greltz cell modules, also called Dye-Sensitized Solar Cells (DSSC), for which exposure to moisture can cause, in addition to deterioration of the electrodes, dysfunction of the electrolyte by inducing electrochemical parasitic reactions. A preferred method of manufacturing a layered element according to the invention, comprising a polymer layer and a multilayered barrier layer of hydrogenated silicon nitride against at least one side of the polymer layer, comprises depositing the or each barrier layer. by plasma enhanced chemical vapor deposition (PECVD). This technique of deposition under reduced pressure involves the decomposition of precursors under the effect of a plasma, in particular under the effect of collisions between the excited or ionized species of the plasma and the molecules of the precursor. The plasma can for example be obtained by a radiofrequency discharge created between two plane electrodes (RF-PECVD), or with the aid of electromagnetic waves in the microwave domain (MWPECVD). Microwave PECVD technique using coaxial tubes to generate the plasma has the advantage of allowing the deposition on a large film running, with particularly high deposition rates. The PECVD technique is particularly advantageous for the manufacture of a layered element according to the invention because it makes it very easy to obtain a variation of the density and the stoichiometry of a layer, by modifying one or more magnitudes among, in particular, the pressure in the enclosure of the deposit, the power, or the relative proportions of the precursors. In particular, the increase of the pressure in the deposition chamber generally favors the formation of less dense layers. It is thus possible to vary the pressure during the deposition to obtain correlatively a variation in density and stoichiometry. An increase in power can cause an increase in the density of the layer. In addition, a modification of the relative proportions of the precursors may lead to a change in the stoichiometry of the constituent material of the layer, impacting the refractive index and / or the density of the layer. According to a less preferred variant, the or each multilayer barrier layer may be deposited on the polymer substrate by cathode sputtering, in particular assisted by a magnetic field, by varying during the deposition one or more of the following quantities: the pressure in the enclosure of the deposit, power. An increase in pressure, as in the case of PECVD, favors the formation of less dense layers. Other deposition techniques are possible, but are less preferred, including evaporation techniques, or atmospheric pressure PECVD processes, particularly those using dielectric barrier discharge technologies. By way of illustration, in the case of the layered element 11 according to the first embodiment, which comprises the PET substrate 1 and the hydrogenated silicon nitride barrier layer 2, the manufacturing process of the element layered by PECVD comprises steps as described below. In an RF-PECVD deposition chamber under reduced pressure, the substrate 1 is introduced into PET. The face 1A of the substrate 1 is then activated by means of a plasma, in particular an O 2 or H 2 plasma, in order to clean the face 1A of the substrate and to improve the adhesion of the barrier layer 2 on this face. . The precursors for the deposition of the SiNXHy type barrier layer 2 are an SiH4 / NH3 mixture diluted in an N2 / H2 mixture. This dilution allows a better stabilization of the plasma, while contributing to the physicochemical properties of the barrier layer obtained. The deposit is made in four successive steps. In a first step, the pressure in the chamber is set at 400 mTorr, the pfd deposited by the plasma being 0.15 W / cm 2. In a second step, the pressure is gradually increased to 600 mTorr, the power being 0.10 W / cm 2. The third and fourth steps are identical respectively to the first and second steps. In order to obtain the density gradient junction zones, the plasma is not interrupted and the pressure and power parameters are continuously modified between the deposition steps of the two successive thin layers of each pair of thin layers. successive layers of the stack of the barrier layer 2. In other words, a continuous increase ramp of the pressure and a ramp of continuous decrease of the power are applied, the duration of these ramps being adapted to obtain the thickness geometric desired of each junction zone 20.

The deposition of the barrier layer 2 on the substrate 1 is carried out at a temperature close to ambient, below 100 ° C. The hydrogenated silicon nitride barrier layer 2 of suitable thickness is thus obtained, which can be subdivided into four successive sublayers 21 to 24 each corresponding to a deposition step. The refractive index and the density are stronger in the first and third layers 21 and 23 than in the second and fourth layers 22 and 24. The production of the layered elements 111, 211 according to the second and third embodiments is operates according to methods similar to that described above for the layered element 11, by depositing the barrier layers 103, 202, 203 on the corresponding faces of the substrate 101 or 201. In the case of the layered element 311 of the fourth embodiment, the barrier layer 302 is deposited on the layer 305 of AZO according to a method similar to that described above for the layered element 11, the lamination interlayer 304 then being deposited on the barrier layer 302.

Claims (15)

REVENDICATIONS1. Layered element (11; 111; 211; 311) for encapsulating an air-sensitive and / or moisture-sensitive element (12; 13; 312), especially a radiation-collecting element or emitter such as a photovoltaic cell or an organic light-emitting diode, the layered element comprising a polymer layer (1; 101; 201; 304) and a barrier layer (2; 103; 202,203; 302) against at least one face (1A; 101B; 201A, 201B; 304A) of the polymer layer, characterized in that the or each barrier layer (2; 103; 202,203; 302) consists of a stack of at least two thin layers (21,22,23). , 24; 131, 132; 221, 222, 231, 232; 321, 322, 323, 324) of hydrogenated silicon nitride having alternatively lower and higher densities. 2. Layered element according to claim 1, characterized in that the or each barrier layer (2; 103; 202, 203; 302) comprises, at the interface between a first layer and a second layer of each pair of thin layers. successive layers of its constituent stack, a junction zone (20; 130; 220; 230; 320) having a density gradient between the density of the first layer and the density of the second layer. Layered element according to claim 1 or 2, characterized in that the difference between the density of a layer of higher density and the density of a layer of lower density of each pair of thin layers. successive layers of the constituent stack of the or each barrier layer (2; 103; 202, 203; 302) is greater than or equal to 10% of the density of the layer of lower density. 4. Layered element according to any one of the preceding claims, characterized in that it comprises a barrier layer (2; 202; 302) against the face (1A; 201A; 304A) of the polymer layer (1; 201; 304) intended to be directed towards the sensitive element (12; 13; 312) and / or a barrier layer (103; 203) against the face (101 B; 201 B) of the polymer layer intended to be directed to the opposite of the sensitive element (12; 13; 312). A layered element according to any one of the preceding claims, characterized in that the polymeric layer is a thermoplastic polymer substrate (1; 101; 201) which has a barrier layer (2; 103; 202,203; 302) on at least one of its faces (1A; 101B; 201A, 201B). 6. Layered element according to any one of claims 1 to 4, characterized in that the polymer layer is a lamination interlayer (304) which has a barrier layer (302) against at least one of its faces (304A). 7. layered element according to any one of the preceding claims, characterized in that the polymer layer (1; 101; 201; 304) and the or each barrier layer (2; 103; 202,203; 302) are transparent, the geometric thickness (e21, e22, e23, e24, e131, e132, e221, e222, e231, e232, e321, e322, e323, e324) of each thin layer of the or each barrier layer (2; 203; 302) being adapted to maximize the transmission of radiation through the layered element (11; 111; 211; 311) to or from the sensing element (12; 13; 312) by an anti-reflective effect. . 8. Layered element according to claim 7, characterized in that the constituent stack of the or each barrier layer (2; 103; 202, 203; 302) comprises at least the superposition of a thin layer of hydrogenated silicon nitride. of refractive index between 1.8 and 1.9 at 550 nm and a thin layer of hydrogenated silicon nitride of refractive index between 1.7 and 1.8 at 550 nm. 9. Device (50; 60; 350) comprising an element (12; 13; 312) sensitive to air and / or moisture, characterized in that it comprises a layered element (11; 111; 211; 311) according to any one of the preceding claims as a front and / or rear encapsulation element of the sensing element (12; 13; 312). 10. Device according to claim 9, wherein the sensing element is a radiation collecting or emitting element (12; 13; 312) which is arranged with respect to the layered element in such a manner that to be able to collect radiation passing through the polymer layer (1; 101; 201; 304) and the or each barrier layer (2; 103; 202,203; 302), or to emit radiation through the polymer layer and the or each barrier layer. 11. Device according to claim 10, characterized in that the collector element or radiation emitter is a photovoltaic cell (12 312) or an organic light-emitting diode (13). 12. A method of manufacturing a layered element (11; 111; 211 311) according to any one of claims 1 to 8, characterized in that at least a portion of the thin layers of the stack constituting the or each barrier layer (2; 103; 202, 203; 302) by plasma enhanced chemical vapor deposition (PECVD) and / or sputtering. 13. Manufacturing process according to claim 12, characterized in that at least a portion of the thin layers of the constituent stack of the or each barrier layer (2; 103; 202, 203; 302) are deposited by chemical deposition. plasma-assisted vapor phase (PECVD) by varying during the deposition the pressure in the chamber of the deposit and / or the power and / or the relative proportions of the precursors. 14. Manufacturing process according to claim 12, characterized in that at least a portion of the thin layers of the constituent stack of the or each barrier layer (2; 103; 202, 203; 302) are deposited by cathodic sputtering. in particular assisted by a magnetic field, by varying during the deposition the pressure in the enclosure of the deposit and / or the power. 15. Manufacturing method according to any one of claims 12 to 14, characterized in that the thin layers of the constituent stack of the or each barrier layer (2; 103; 202, 203) are deposited on one face ( 1A, 101B, 201A, 201B) of a thermoplastic polymer substrate (1; 101 201) and in that, prior to deposition, said substrate face is activated by means of a plasma.